16.4 Free Energy

16.4 Free Energy

  • The standard entropy change is equal to the difference between the standard entropies of the products and the reactants scaled by their coefficients.

  • An alternative approach involving a new thermodynamic property was introduced in the late 19th century by an American mathematician.

  • There is a relation between the spontaneity of a process and the signs of these indicators.
  • The value of free energy depends on the conditions of the initial and final states of the system that have changed.
    • The calculation of free energy changes for physical and chemical reactions can be done with the use of standard state data.
  • To calculate the standard free energy change for the vaporization of water at room temperature, use standard enthalpy and entropy data from Appendix G.

  • To calculate the standard free energy change for the reaction shown here, use standard enthalpy and entropy data from Appendix G.

  • The free energy change that accompanies the formation of one mole of a substance is called the standard free energy of formation.
    • The approach to computing the free energy change for a reaction is the same one used for enthalpy and entropy changes.

  • Consider how yellow mercury(II) oxide is decomposing.
  • The standard free energies of formation and standard enthalpies of formation are used.
  • Appendix G contains the required data.

  • The temperature of the system may affect the spontaneity of a process.
    • Phase transitions can be done in one direction or the other depending on the temperature of the substance.
    • Some chemical reactions can be temperature dependent.
  • The absolute temperature and the enthalpy of the free energy change are two of the signs of the process's spontaneity.
  • An increase in system entropy is described in this condition.
  • This condition describes an exothermic process.
  • This condition describes an endothermic process.
  • This condition describes an exothermic process.
  • There are four possibilities for the signs of enthalpy.

  • It is important to keep in mind what the terms "high" and "low" mean when considering the temperature dependence of spontaneity.
    • The temperatures in question are considered high or low relative to the reference temperature.
  • The two yellow lines in the plot show the temperature-dependence of the plot's enthalpy and entropy changes.
  • This condition describes a system at equilibrium.
  • When vaporization and condensation occur at equal rates, the boiling point of a liquid is the temperature at which its solid and liquid phases are in equilibrium.
  • The boiling point of water can be estimated using the information in Appendix G.

  • The accepted value for water's boiling point is 371.2 K (100.0 degC), and so this calculation is reasonable.
    • Standard data was used to derive the values for enthalpy and entropy changes.
    • If desired, you could get more accurate results by using enthalpy and entropy changes that are closer to the boiling point.
  • The information in Appendix G can be used to estimate the boiling point.
  • The free energy change may be seen as a measure of the process's driving force.

  • calculate the free energy change for this same reaction in a mixture of 0.
    • 100 mol of each gas.

  • This form of the equation can be used to derive equilibrium constants from standard free energy changes and vice versa.
  • At equilibrium, products are more abundant.
  • At equilibrium, reactants are more abundant.
  • At equilibrium, reactants and products are equally abundant.

  • The result is in agreement with the value in Appendix J.
  • The equilibrium constant for the dissociation of dinitrogen tetroxide is calculated using the data provided in Appendix G.
  • The observation that reactions spontaneously proceed in a direction that establishes equilibrium is an example of the relation between these two essential concepts.
  • The system's free energy is minimized in Chapter 16.
  • The plots show the free energy versus reaction progress for systems with standard free changes.
    • In order to minimize free energy and establish equilibrium, nonequilibrium systems will proceed spontaneously.

  • Under certain conditions, chemical and physical processes tend to occur in one direction.
    • A nonspontaneous process requires a constant input of energy from an external source, while a spontaneously occurring process does not.
    • A change in the way matter and/or energy is distributed within the system can be experienced by systems undergoing a spontaneously occurring process.
  • It can be seen as a measure of the dispersal or distribution of matter and/or energy in a system.
  • When a system is heated, entropy increases.
  • Some chemical reactions may be predicted using these guidelines.
  • The zero for entropy is established by the third law of thermodynamics.
    • The standard entropy change can be calculated by using the reactants and products involved in the process.
  • There are many approaches to the computation of free energy changes.
  • The following processes may be nonspontaneous.
  • He atoms diffuse through the wall of a balloon as it spontaneously deflates.
  • Carbon and hydrogen are found in many plastic materials.
    • Plastic materials tend to persist in the environment even though they have been oxidation in the air to form carbon dioxide and water.
  • The halogens have an increase in their entropy at room temperature.

  • There is a reason for your prediction.

  • Under standard state conditions, it is possible to give gaseous carbon dioxide and liquid water.
  • Under standard state conditions, determine the change in the entropy for the burning of propane, C3H8.
  • Thermite reactions have been used for welding and metal refining.
    • The surroundings absorb 851.8 kJ/mol of heat during the reaction.

  • All are run under the same conditions.
  • All are run under the same conditions.
  • To determine the free energy change for each reaction, use the standard free energy data in Appendix G.

  • Under standard state conditions, consider the decomposition of red mercury(II) oxide.
  • An ideal fuel for the control thrusters of a space vehicle should break down in an exothermic reaction when exposed to the appropriate catalyst.
    • The following substances should be evaluated as suitable candidates for fuels.

  • This information can be used to calculate the standard free energy change for the reaction of hydrogen ion with hydroxide ion to produce water.
  • Natural gas contains hydrogen sulfide.
  • acetylene can be used to make Benzene.
    • Determine the equilibrium constant at 25 and 850 degrees.
  • Carbon dioxide and O2 are created at elevated temperatures.
  • Carbon tetrachloride is prepared by chlorination of methane at 850 K.
  • In the gas phase, acetic acid, CH3CO2H, can form a dimer.
  • The equilibrium constant for the dimerization is 1.3 x 103.

  • Determine the standard enthalpy change, entropy change, and free energy change for the conversion of diamond to graphite.
  • The standard free energy change for a mole of water is 8.6 kJ.
  • The H2O is at 0.011 atm.
  • The temperature is 37 degrees.
  • When the temperature is increased, determine which of the following will reduce the free energy change for the reaction, that is, make it less positive or more negative.
  • The solution when added to water and stirred feels cold.
  • chalcocite is a form of copper(I) sulfide and is an important source of copper.
  • If you combine the equations from Parts (a) and (b), you can explain why the roasting of chalcocite makes for a more efficient process for the production of copper.